Speaker systems for reproducing recorded sounds and particularly recorded music have long been available. These systems generally comprise one or more acoustic transducers or speakers mounted in an enclosure that enhances the sounds produced by the speakers. Speaker systems are available in various sizes and designs with many having one speaker for reproducing lower and midrange audio frequencies and a second speaker for reproducing higher audio frequencies.
While prior art speaker systems are adequate reproducers of recorded sounds, certain types of audio distortion that degrade the quality of the reproduced sounds are commonly introduced by the operation of the speaker system itself. Examples of such distortions are intermodulation or IM distortion resulting from doppler frequency shifts of midrange audio frequencies produced by a speaker cone that is also producing low audio frequencies, frequency phase shift resulting from the production of sound by a non flat speaker cone or diaphragm; asymmetric propagations of sound due to different sounds being reproduced by different portions of the speaker diaphragm; and resonant "boom". Low frequency sounds can also be enhanced near the natural resonant frequency of the speaker system introducing a box like or "booming" quality into the reproduced sound. These problems can be especially acute in small so-called "book shelf" speaker systems.
Attempts have been made to reduce the audio distortions discussed above. Such attempts include acoustical loading of the speaker, varying the density of the speaker diaphragm from its center to its edges, providing slots or grooves in the speaker diaphragm, and providing speakers with flat diaphragms or membranes for reproducing sound. Examples of such attempts can be found in U.S. Pat. Nos. 4,387,787 of King, 1,882,974 of Schlenker, 1,990,409 of Lawrance, and 4,029,171 of Manger.
While some of the above attempts have improved the quality of sound reproduced by speaker systems, they have not been entirely successful because each technique typically addresses only one type of distortion and may even enhance other types.
Accordingly, it is to the provision of a speaker system that greatly reduces the types of distortion discussed above resulting in much improved reproduced sound quality that the present invention is primarily directed.